Effect Of Morphology Tuning And Rare Earth Ions Doping On Oxygen Vacancy And Photocatalytic Performance Of Hydrogen Annealed Nanoceria

The photocatalytic application of ceria is hindered by a wide energy band gap and a high recombination rate of photogenerated electrons（e^-）and holes（h⁺）.Introducing oxygen vacancies in ceria lattice has an innegligible effect on the photocatalytic performance of ceria.However,the influence on energy band gap,photocarriers characteristic and photocatalytic preformance of oxygen vacancies producing by morphology tuning,additional cations doping or annealing in H₂ still need further investigation.In this work,polyhedral,cubic,rod-like nanoceria or different length of nanorod ceria were synthesized,and doped La,Y and Sm ions in a certain samples.H₂-TPR was used to analyze the redox ability of ceria with different morphology,size and doping Y element.XRD,TEM,XPS,UV-Vis DRS,PL spectra and the test of photocatalytic degradation of methylene blue solution et.al were used to investigate the phase,morphology,oxygen vacancy concentration,energy band structure,the combination rate of photogenerated e^-and h⁺,and the photocatalytic mechanism of hygrogen annealed nanoceria with morphology tuning and rare earth ions doping.The research found that the surface oxygen vacancy concentration increases with the increasing concentration of H₂in annealing atmosphere.The rod-like nanoceria is more easily reduced by H₂ at a low temperature.With the increase of surface oxygen vacancy concentration,the UV-Vis DRS spectra of polyhedral,cubic,rod-like nanoceria firstly bule shift and then red shift.The separation and recombination efficiency of photogenerated carriers are improved with the increasing of surface oxygen concentration which makes a significant contribution to photocatalytic performance of nanoceria.The polyhedral,cubic,rod-like nanoceria annealing in H₂ has an excellent photocatalytic performance,and the degradation rate is 93.82,85.15 and 90.09%.In addition,the surface oxygen vacancy concentration of nanorod ceria annealing in H₂ firstly increase and then decrease with the increasing length of nanorod,while the energy band gap increases gradually with the increasing of surface oxygen vacancies and length of nanorod ceria.The sample with a length of 114 nm and a diameter of 10 nm has a higher oxygen vacancy concentration and a lower recombination rate of photogenerated carriers after H₂ annealing,which shows a higher photocatalytic performance,and the degradation rate is 86.32%.Doping lanthanum,yttrium and samarium ions can narrow the band gap of polyhedral,cubic and rod-like nanoceria and reduce the recombination rate of photogenerated carriers,and the photocatalytic performance of each studied morphology of nanoceria can be significantly improved.Among all the samples,10%is the best doping amount and yttrium is the optimal doping element.The 10%yttrium doped nanorod ceria has a higher Ce³⁺concentration and exhibits a better photocatalytic degradation activity,and the degradation rate is 85.59%.The surface oxygen reduction temperature of polyhedral,cubic and rod-like nanoceria is decreased by doping yttrium ions,which further improves the stability of morphology.The band gap of yttrium doped nanoceria with studied morphologies decreased after annealing in H₂ at 600 ^oC.With the increase of surface oxygen vacancy concentration,the photocatalytic activity of yttrium doped nanoceria with various morphologies is gradually improved,and the degradation rate of nanorod ceria annealing in H₂ is improved by 18.5%comparing with the sample annealing in air.